Effect of aging on regional neuromuscular regulation within human rectus femoris muscle during stair ascent and descent

Our recent studies showed the rectus femoris (RF) muscle is regionally regulated during the level walking and this unique neuromuscular activation pattern is influenced by aging (Watanabe et al., 2014, 2016 J Biomech). We aimed to investigate and compare regional neuromuscular activation patterns along the RF muscle between the young and elderly during the stair walking. Fourteen young men (age: 20.4 ± 1.0 years) and 14 elderly men (age: 73.8 ± 5.9 years) performed the stair ascent and descent. Fifteen trials of three steps were performed for both stair ascent and descent. The spatial distribution of surface electromyography (EMG) within the RF muscle was assessed by central locus activation (CLA), which is calculated from 18 surface electrodes along the longitudinal line of the muscle. CLA was significantly moved along the muscle during the stair ascent and descent in both young and elderly (p < 0.05). Significant differences in CLA were showed at the stance phase of the ascent (12.5 ± 0.7 and 11.4 ± 1.7 cm from most proximal electrodes for the young and elderly, p < 0.05) and at the swing phase of the descent (11.4 ± 1.5 and 10.3 ± 1.5 cm from most proximal electrodes for the young and elderly, p < 0.05). These results suggest that the regional neuromuscular activation within the RF muscle is affected by aging during the stair walking.